The deposition of InAs on GaAs proceeds first by two-dimensional (2D) growth and above a 1.75-monolayer coverage by the formation of single-crystal dots on a residual 2D wetting layer. By atomic force microscopy measurements, we show that the first dots formed are in the quantum size range (height 30 Å, half-base 120 Å), that the dispersion on their sizes is remarkably low (±10%), and that they are located fairly regularly (interdot distance 600 Å). Upon further growth, density and shapes do not change but sizes increase up to double values before coalescence occurs. Self-organized growth in strained structures is then shown to be a simple and efficient way of building regular quantum dots.

A parametric study of single-crystal silicon roughness induced by an SF6 plasma has been carried out by means of atomic force microscopy. An helicon source (also called resonant inductive plasma etcher) has been used to study the relation between plasma parameters and subsequent surface damage. The surface damage has been examined in terms of height roughness analysis and in terms of spatial (lateral) extent of the surface roughness. The central result is that roughness scales with the ratio of the ion flux over the reactive neutral flux (J+/JF), showing the combined role of both ionic and neutral species. At low ion flux, the neutrals smooth the surface, while at higher ion flux, they propagate the ion-induced defects, allowing the roughness to be enhanced. Influences of other parameters such as exposure duration, ion energy, or substrate temperature have also been quantified. It is shown that the roughness growth is well described by an empirical law: rms∝(1/√E)(J+/JF)ηtβ, with η≊0.45 and β≊1 (rms is the root mean square of the roughness). In other respects, we analyze the data with a Fourier transform analysis. The main advantage is to minimize noise and to separate the magnitude of the roughness, the lateral correlation length on which the roughness is growing, and the behavior of short and long range roughness. The results are identical to the rms analysis, especially, the above scaling law. The time evolution of the lateral correlation length follows a scaling law (which is not accessible by means of the rms) leading to a fractal dimension of 2.67. Also is observed a variation of the short range roughness as a function of the substrate bias voltage. Consequence for further scaling down of integrated circuits is called to mind.

Cross characterizations of surface roughness of glassy materials have been performed using Atomic-Force Microscopy (AFM) and optical scattering techniques. The AFM measurements provide images of the surface height contours from the micrometer down to the nanometer scale. From a two-dimensional (2D) Fourier analysis of the images, the roughness power spectrum is measured for a range of spatial frequencies from 0.04 pn-' up to 400 p-'. An excellent agreement ia obtained with parallel light scattering measurements of the surface roughness over the spatial frequencies ranging from 0.05 pn-' to 1.54 pn-', corresponding to the overlap bandwidth reached by the two techniques. From the power law dependence of the roughness spectrum vs. spatial frequency found on the whole range of AFM analysis, fractal properties of this self-afthe surface are discussed.* * * PH. DUMAS and F. SALVAN are particularly grateful for stimulating discussions with W. PRESS, J. CHEWER and V. PANELLA They acknowledge E. D. WILLIAMS for rising our attention to prior works studies using near-field microscopy.

The diffusion of boron in N2 ambient is studied by using p+ polysilicon metal-oxide-silicon structures annealed during times long enough to allow boron diffusion through the gate oxide, up to the underlying substrate. Assuming equilibrium segregation at the interfaces, the boron diffusivity in the oxide is calculated by numerically fitting the resulting profile in the substrate. It is found that B diffuses in SiO2 with an activation energy of about 3 eV. We also quantify the influence of the nitridation of the oxide, and confirm its efficiency as a diffusion barrier. However, this study reveals a strong inconsistency between the extracted diffusivity values of B in SiO2 and the amount of B atoms being able to reach the Si/SiO2 interface to account for the observed interface state density.

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